DESCRIPTION: The central nervous system (CNS) controls the kidney via coordination of the autonomic nervous system (the visceral neuraxis). Functional work has revealed a role for the neural circuitry of the kidney in the development and/or maintenance of several models of experimental hypertension. In addition, the kidney is crucial for maintenance of body fluid homeostasis via control of sodium and water retention. Other work has suggested a role for renal afferents and renal efferents in the development/maintenance of various experimental models of hypertension. Despite these important roles in cardiovascular control and hypertension, little is known about the CNS circuitry controlling the kidney, e.g., how renal control circuitry is integrated with the circuitry subsuming fluid homeostasis. Several neuroanatomical tract tracing studies have clearly defined the "final common pathway" of efferent neurons and described the location of first order renal afferents. To understand how the kidney is involved with neural circuitry controlling fluid homeostasis, knowledge of the intervening circuitry is necessary. Here the neural circuitry controlling the kidney will be studied in two ways: 1) the output pathway will be labeled via the retrograde trans-synaptic transport of a neurotropic virus and 2) the renal input pathway will be traced using an immunocytochemical technique for the activity-related protein product of the proto-oncogene, c-fos in stimulated neurons and via transneuronal transport of neurotropic virus. In subsequent experiments, the functional organization of renal circuitry will be elucidated. It is expected that these techniques will label neurons which are directly involved with kidney plus second order (or possibly third order) neurons belonging to the renal control circuit. Specific dissection of the afferent and efferent pathway will be coupled with the above mentioned tract tracing methods to confirm the specificity of our technique. The results of these experiments will provide a more complete picture of the neural circuitry involved with renal control and may suggest sites involved with pathological states such as hypertension.